Technical Field
The present invention relates to photovoltaic devices, and more particularly to photovoltaic devices and methods having a double layer transparent conductive oxide to reduce barrier height.
Description of the Related Art
A solar cell may be formed on a glass substrate and may include an electrode (metal) formed in contact with a p-type layer (semiconductor). The electrode may include a transparent film that is conductive, or a transparent conductive oxide (TCO). Currently developed TCOs are n-type since p-type states of TCO are thermodynamically unstable. A Schottky barrier exits between the p-type layer and the TCO. The Schottky barrier is a potential barrier formed at a metal-semiconductor junctions which has rectifying characteristics. The Schottky barrier has a decreased depletion width in the metal. Rectifying properties depend on the metal's work function, the band gap of the intrinsic semiconductor, the type and concentration of dopants in the semiconductor, and other factors.
The Schottky barrier forms as a result of the materials in contact (n-type metal and n-type semiconductor). Due to the n-type nature of TCO, the Schottky barrier always exists at the interface between the p-type semiconductor and TCO. The Schottky barrier at this location in undesirable and degrades performance.